A mouse must be distinguished from other cursor control systems, such as light pens and interactive tablets. These are devices in which electrical or electromagnetic energy is communicated from a wand or other movable member to energy receptors within an active surface, grid or the like. On the other hand, a mouse moves over a passive surface, such as a sheet of paper, or the like.
A mouse must also be distinguished from a joy stick control. A joy stick includes a lever, usually connected to a bearing. As the lever is moved and the bearing is rotated correspondingly. Bearing motion is sensed by potentiometers corresponding to different directions of bearing rotation. The output signal from a joy stick may be used for the same purpose as the output signal from a mouse. Both may be used to control a cursor. The distinguishing feature of a mouse is that two-dimensional motion over a surface corresponds directly with two-dimensional motion of a cursor in a graphic display.
A mouse should also be distinguished from bar code systems. In those systems, bar code is applied to a surface for indicating data, such as type of merchandise, price and manufacturer. The bar code typically produces an analog signal which may be read optically or magnetically. In U.S. Pat. No. 4,245,152 to Flurry et al., an ETAB (every transition a bit) code is described. Such systems do not yield positional information, as mice do.
Most of the mice of the prior art are mechanical systems involving wheels or rollers which maintain frictional contact with a surface. For example, U.S. Pat. No. 3,541,541 to D. Engelbart shows a well-known and widely accepted mechanical mouse. There are certain mechanical problems which are inherent with these mice, such as the problem in maintaining good frictional contact with a surface. If a mechanical mouse encounters a slippery portion of a surface, the resulting output signal will be inaccurate.
Mechanical mice use a relatively large number of close tolerance parts and are difficult to make in mass production. Moreover, mechanical mice are subject to mechanical "noise", such as lash and vibration, and require frequent cleaning.
An object of the present invention was to devise a non-mechanical mouse, specifically one which relied upon electromagnetic energy transmitted to and radiated back from a surface in order to translate positional motion relative to the surface into an electrical signal for control of a cursor or similar device.